STUDIES OF THE BINDER PHASE IN WC-Co CEMENTED CARBIDES HEAT-TREATED AT 650°C

Abstract

The binder phase of WC-Co cemented carbide is a Co-rich alloy in which tungsten and carbon are in solid solution. The binder phase is supersaturated with respect to tungsten even after slow cooling from the sintering temperature. In this study the binder phase contained 6% W in solid solution before heat-treatment at 650°C (923 K). Transmission electron microscopy on thin foils of binder phase showed that a finely dispersed. phase, α′, precipitated in the cubic binder phase. After long ageing times Co₃W could be identified by X-ray diffraction methods. As no discontinuous , ‘cells’ of Co₃W and ∊-Co could be observed, the following reaction is suggested.

α-Co(W, C)→α-Co+α′→α-Co (C)+Co₃W (needles)

The precipitation of α′ was accompanied by an increase in hardness and a decrease in transverse rupture strength. The effects observed are consistent with those found during annealing of Co-rich cobalt-tungsten-carbon alloys (> 85% Co).

Notes

* Manuscript received 6 September 1971.